Portable transponders employing Radio Frequency Identification (RFID) are used in a variety of applications including to collect highway tolls, to provide personal identification for access control and to provide electronic information interchange, i.e. credit. Passive RFID tags, i.e., tags without internal power sources such as batteries, and wireless cards contain chips, for example computer chips, microchips and memory chips, that store data or information such as identification information, credit card numbers and financial data. These passive tags are applied to items and provide identification information in much the same way as machine-readable optical tags such as bar codes are used. The data or information stored on a tag or wireless card is retrieved using an RFID base station or reader. The reader transmits radio waves that cause the tag or card to transmit information stored on the tag, which is then received and interpreted by the reader. Since the tag or card is a passive device without a source of power, power is derived form the interrogation field transmitted by the reader, e.g., the interrogation field excites a coil within the tag or card.
Examples of passive tags are described in U.S. Pat. No. 3,713,148. In its simplest form the RFID tag includes a circuit, typically in the form of a single silicon chip although more than one chip may be used in the construction of the RFID tag. This circuit is generally connected to an antenna. The RFID tag is incorporated in a desired device such as an identification tag, a key fob or an identification card. For battery assisted tags, sometimes referred to as semi-passive or semi-active, a battery may also be employed to extend the range of the tag. It is also possible in principle to build devices that function as tags or wireless cards using electrical circuits including only resistors, capacitors and inductors as is well known by those skilled in the art.
One application for RFID is in the tracking of goods as these goods move through the supply chain from manufacturers through retailers to consumers. For example, RFID tagging will be used for point of sale (POS) check out and data collection. For the item tagging application, RFID tags are attached to an item or the packaging of the item that is being inventoried or that is being offered for sale. The tag in many cases remains attached to the item after that item has been sold to a customer. Since the tag is still active, that tag can be read after sale while the item is in the possession of the consumer, raising consumer privacy concerns. One method to alleviate these concerns is to deactivate or to disable the RFID tag after sale without actually having to physically remove the tag.
The EPCglobal Generation 2, Gen2, RFID protocol includes a kill command that renders the tag inoperable. This kill command is often referred to as a “Privacy” command, which can be used to permanently deactivate the device at the end of its working life, for example as a customer leaves a store. However, there are problems associated with the kill command. For example, if the kill command permanently disables a tag, then the tag may not be used for future applications including use of the tag for recalls or returns.